This invention relates to electric motors which are utilized outdoors. More specifically, this invention relates to the use of electric motors out of doors where such motors will be operated intermittently over long periods of time without servicing or attention. A number of situations require the use of electric motors in outdoor environments, as for example, air-cooled house air conditioning units, electric lawn mowers and the like. One industrial application of an electric motor outdoors is for driving various irrigation devices on acreage under cultivation. A large number of irrigation devices exist which are operated by electric motors deployed in a field which are selectively operated during the growing season to irrigate the acreage. Generally such motors are used to drive the irrigation devices from a previous position to a new position in order to fully irrigate the acreage. Such motors, subjected to severe weather and dust conditions, are operated intermittently and receive very little care and attention between servicing intervals.
In order to obtain satisfactory service from such motors, it is necessary to protect them from the dust and moisture. It has been found that the motor housing which encloses the windings and drive shaft does not act as a sufficient moisture barrier. When a motor is operated for a period of time it warms up. If it is then shut off for a considerable length of time, any moisture such as rain, snow, etc., which contacts the motor housing causes condensation on the inside of the motor housing. This condensation will build up and collect in the bottom of the motor housing, causing ultimate and premature failure of the motor due to water in the windings.
An additional problem encountered, where only the housing is utilized to protect the motor, is that water will collect on top of the motor when not operating. Subsequent motor start-up, particularly where the motor is mounted vertically, will exert a slight negative pressure in the area of the drive shaft bearing directly beneath the motor cooling fan. This negative pressure is responsible for encouraging seepage of moisture between the bearing and shaft which ultimately collects inside the motor housing further aggravating the moisture problem.
Accordingly, in order to protect the motor for a substantial period of time, it is necessary to provide an enclosure in addition to the motor housing which not only prevents moisture from getting into the motor, but also keeps moisture from contacting the motor housing.
A constraint upon providing such an enclosure is that it is necessary that the motor be fan cooled during its period of operation, and accordingly an air flow into and out of the enclosure is necessary in order to prevent excessive heat buildup. A prior patent which has considered the problem and offered a solution thereto is U.S. Pat. No. 2,777,079. In this patent a horizontally mounted outdoor motor is disclosed which is maintained substantially weatherproof but which is ventilated by air circulation. This patent discloses a large housing structure wherein air is pulled in through a side housing and circulated directly through openings in the motor housing into the motor rotor and stator windings for cooling purposes. There is no concern with preventing moisture from contacting the motor housing nor is the design particularly desirable for smaller vertically mounted motors utilized for irrigation applications.
It is accordingly an object of the present invention to provide an outdoor motor enclosure for electric motors which will prevent moisture from impinging upon a motor housing while permitting adequate air cooling.
It is another object of the present invention to provide an outdoor motor enclosure which will prevent moisture from accumulating on the top of the motor housing between operating periods, whereby subsequent operation of the motor could cause such moisture to be drawn inside the motor housing.
It is another object of the present invention to provide a compact outdoor motor enclosure for protecting an electric motor which is vertically mounted with the cooling fan on the upper end thereof.
Other objects and advantages of the invention will be apparent from the concluding portion of the specification.